A warm sleeping bag is essential to any camping or backpacking trip, especially in cold weather. To this end, many sleeping bags have been produced with lightweight and warm insulation. One problem with such sleeping bags is that, although they are generally warm, because they have fixed weights of insulation distributed evenly throughout them, there can be areas of a person's body, ‘cool spots’, that remain cool or cold while other body parts are warm. For example, the area surrounding the feet may be such a cool spot.
Therefore, a sleeping bag that provides additional thermal insulation at a designated area is needed.